Method and a system for sealing an epitaxial silicon layer on a substrate

ABSTRACT

A system for processing a wafer is provided. Ultraviolet light radiates through a first amount of oxygen gas in an ozone generation chamber so that the first amount of oxygen gas is converted to a first amount of ozone gas. The first amount of ozone gas flows from the ozone generation chamber into a loadlock chamber and a wafer is exposed to the first amount of ozone gas. The ultraviolet light also radiates through a window and then through a second amount of oxygen gas in the loadlock chamber so that the second amount of unconverted gas is converted to a second amount of ozone gas. The wafer held by the wafer holder is also exposed to the second amount of ozone gas.

BACKGROUND OF THE INVENTION

[0001] 1). Field of the Invention

[0002] This invention relates to a method of and a system for sealing anepitaxial silicon layer formed on a semiconductor wafer.

[0003] 2). Discussion of Related Art

[0004] Integrated circuits are formed in and on silicon and othersemiconductor wafers. Wafers are made by extruding an ingot from asilicon bath and sawing the ingot into multiple wafers. In the case ofsilicon, the material of the wafers is monocrystalline. An epitaxialsilicon layer is then formed on the monocrystalline material of thewafer. The epitaxial silicon layer is typically doped with boron and hasa dopant concentration of about 1×10¹⁶ atoms per centimeter cube. Atypical epitaxial silicon layer is about five microns thick. Thematerial of the epitaxial silicon layer has better controlled propertiesthan the monocrystalline silicon for purposes of forming semiconductordevices therein and thereon.

[0005] Once the epitaxial silicon layer is formed, the wafer is removedfrom the wafer processing chamber and exposed to ambient air. The airoxidizes the exposed epitaxial silicon layer to form a native oxidelayer thereon. The epitaxial silicon layer and the native oxide layerare exposed to contaminants in the air and are usually filled withimpurities and particles. When semiconductor devices are formed on asurface which is filled with impurities, the electronic devices oftenfail.

[0006] It has been suggested that exposure of an epitaxial silicon layerto ozone gas will provide an efficient process for forming a very pureoxide layer on the epitaxial silicon layer. Furthermore, U.S. patentapplication Ser. No. 09/350,805 describes a system which is used toprocess a wafer so that an epitaxial silicon layer is formed thereon,followed by exposure to ozone gas in a loadlock chamber. The wafer ishowever exposed with other wafers and exposure takes at least 20minutes. Such slow exposure may inhibit a process where only a fewwafers are processed.

SUMMARY OF THE INVENTION

[0007] A system for processing a wafer is provided comprising a chamberbody, a window, a wafer holder, an ozone generation chamber, and atleast one ultraviolet lamp. The window is transmissive to ultravioletlight and is mounted to the chamber body. The chamber body and thewindow jointly form a chamber. The chamber defines an enclosure and hasat least a first opening for transferring a wafer therethrough from anarea externally of the chamber into the enclosure. The wafer holder islocated within the chamber to hold the wafer in the enclosure. The ozonegeneration chamber is located externally of the chamber and is incommunication with the enclosure. The ultraviolet lamp has a filamentwhich, when electric current flows therethrough creates ultravioletlight. The ultraviolet light therefrom radiates through a first amountof unconverted gas in the ozone generation chamber so that the firstamount of unconverted gas is converted to a first amount of ozone gas.The first amount of ozone gas flows from the ozone generation chamberinto the enclosure and the wafer held by the wafer holder is exposed tothe first amount of ozone gas. The ultraviolet light also radiatesthrough the window and then through a second amount of unconverted gasin the enclosure so that the second amount of unconverted gas isconverted to a second amount of ozone gas. The wafer held by the waferholder is also exposed to the second amount of ozone gas.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention is further described by way of example withreference to the accompanying drawings wherein:

[0009]FIG. 1 is a plan view of a system for processing a wafer;

[0010]FIG. 2 is a diagram of a loadlock assembly forming part of thesystem and illustrates a loadlock chamber thereof in sectioned sideview;

[0011]FIG. 3 is a flow chart of how the system is operated;

[0012]FIG. 4 is a time chart of how the system operates;

[0013]FIG. 5 is a cross-sectional side view of a wafer which isprocessed according to the invention;

[0014]FIG. 6 is a cross-sectional end view of an ozone generator whichis used in the loadlock assembly;

[0015]FIG. 7 is a cross-sectional side view of the ozone generator;

[0016]FIG. 8 is a graph of ozone concentration against backfill rate;

[0017]FIG. 9 is a graph of oxide formation against ozone concentration;

[0018]FIG. 10 is a cross-sectional side view of a portion of a loadlockassembly used in a system, for processing a wafer, according to analternative embodiment of the invention;

[0019]FIG. 11 is a cross-sectional end view of an ozone generator on11-11 of FIG. 10;

[0020]FIG. 12 is a graph illustrating concentration levels of air, afirst amount of ozone gas generated in the ozone generation chamber, anda second amount of ozone gas generated in a loadlock chamber of theloadlock assembly of FIG. 10;

[0021]13 is a cross-sectional side view of the loadlock assembly of FIG.10, illustrating more components thereof;

[0022]FIG. 14 is a cross-sectional end view of the loadlock assembly ofFIG. 13;

[0023]FIG. 15 is a diagramatic representation of one method in which theloadlock assembly of FIGS. 10 to 14 can be used; and

[0024]FIG. 16 is a diagramatic representation of another method in whichthe system can be used.

DETAILED DESCRIPTION OF THE INVENTION Batch-Exposure to LowConcentration Levels of Ozone Gas Suitable for Epitaxial SiliconDeposition on a Large Number of Wafers

[0025] The present invention relates to a method whereby an epitaxialsilicon layer formed on a silicon wafer is sealed with an oxide formeddue to exposure to ozone gas. A plurality of the wafers are located in abatch in a loadlock chamber and exposed to ozone gas under controlledconditions. The ozone gas forms a stable and clean oxide layer on theepitaxial silicon layer of each wafer. The oxide layer can later beremoved to leave the epitaxial silicon layer exposed and containingsubstantially no impurities. There are certain advantages for processingthe wafers in the loadlock chamber. One advantage is that anotherchamber which is designated for a step in an existing process does nothave to be dedicated for exposing the wafers to ozone gas. Anotheradvantage is that such a system is relatively safe because there is asubstantially reduced likelihood that the ozone gas will mix withhydrogen gas within the system and cause an explosion, in particularbecause the pressure within the loadlock chamber is lower than a chamberin the system where hydrogen gas is used. The system is also safebecause the pressure within the loadlock chamber is always belowatmospheric pressure of an area around the loadlock chamber when ozonegas is within the loadlock chamber so that there is reduced likelihoodthat the ozone gas will escape to a surrounding area and cause anexplosion. Another advantage is that the overall time taken to processwafers is maintained.

[0026]FIG. 1 of the accompanying drawings illustrates a system 10 forprocessing a semiconductor wafer. The system 10 is of the kind sold asthe Epi Centura system sold by Applied Materials of Santa Clara, Calif.The system 10 includes a factory integration unit 12, first and secondbatch loadlock assemblies 14A and 14B, a transfer chamber 18, first,second, and third wafer processing chambers 20A, 20B, and 20C, and acooldown chamber 22.

[0027]FIG. 2 illustrates one of the loadlock assemblies 14 in moredetail. The loadlock assembly 14 includes a loadlock chamber 24, acassette elevator 26, a wafer cassette 28, a pump 30, and apparatus 32for supplying gasses into the loadlock chamber 24.

[0028] The loadlock chamber 24 defines an enclosure 34 and has a dooropening 36 on one side thereof and a slitvalve opening 38 on an opposingside thereof. The factory integration unit 12 mates with the loadlockchamber 24 over the door opening 36. A door 40 is mounted to theloadlock chamber 24 for movement between a position as shown in FIG. 2wherein the door 40 closes the door opening 36, and a position whereinthe door opening 36 is open so that the confines of the factoryintegration unit 12 are in communication with the enclosure 34.

[0029] The transfer chamber 18 mates with the loadlock chamber 24 overthe slitvalve opening 38. A slitvalve 42 is mounted to the loadlockchamber 24 for movement between a position as shown in FIG. 2 whereinthe slitvalve 42 closes the slitvalve opening 38, and a position whereinthe slitvalve opening 38 is open so that the enclosure 34 is incommunication with the confines of the transfer chamber 18.

[0030] The cassette elevator 26 includes a shaft 44 and a support plate46. The shaft 44 extends through an opening in a base of the loadlockchamber 24. A seal (not shown) is located between the shaft 44 and thebase of the loadlock chamber 24. The support plate 46 is secured to anupper end of the shaft 44.

[0031] The wafer cassette 28 includes a frame 48 with a plurality offins 50 located on the frame. The fins 50 are positioned relative to oneanother so as to be jointly capable of supporting a total of twenty-fivewafers above one another. The wafer cassette 28 is located on thesupport plate 46. The wafer cassette 28 can be elevated by extending theshaft 44 into the loadlock chamber 24, and lowered by retracting theshaft 44 from the loadlock chamber 24. By elevating or lowering thewafer cassette 28, a respective one of the wafers 52 can be aligned withthe slitvalve opening 38 and can be removed from the loadlock chamber 24through the slitvalve opening 38.

[0032] The pump 30 has a low-pressure side 54 and a high-pressure side56. An exhaust line 58 has one end that extends into an opening in abase of the loadlock chamber 24, and an opposed end connected to thelow-pressure side 54 of the pump 30. The pump 30 can therefore be usedfor pumping a gas from the enclosure 34.

[0033] The apparatus 32 includes a source of nitrogen 60, a source ofoxygen 62, an ozone generator 64, a nitrogen supply valve 68, and anozone supply valve 70.

[0034] The source of nitrogen 60 is connected to the nitrogen supplyvalve 68. The nitrogen supply valve 68 is, in turn, connected to anitrogen supply line 74. An opposing end of the nitrogen supply line 74extends into an opening in an upper wall of the loadlock chamber 24.When the valve 68 is open, nitrogen gas from the source of nitrogen 60can therefore be supplied to the enclosure 34. A diffuser (not shown) islocated in the nitrogen supply line 74 to reduce the speed of thenitrogen gas.

[0035] The source of oxygen 62 may, for example, be substantially pureoxygen gas or may be air. It has been found that even filtered air isnot as free of impurities as substantially pure oxygen. The oxygen istypically about 99.999% pure. Substantially pure oxygen may thus bepreferred. The ozone generator 64 is connected to the source of oxygen62.

[0036] When oxygen gas from the source of oxygen 62 is supplied to theozone generator the ozone generator 64 generates ozone gas. The ozonegenerator 64 is, in turn, connected to the ozone supply valve 70. Anozone supply line 76 is connected to the ozone supply valve 70. Anopposing end of the ozone supply line 76 extends into an opening in theupper wall of the loadlock chamber 24. When the valve 70 is open, ozonegas generated by the ozone generator 64 can be supplied to the enclosure34. A diffuser (not shown) is located in the ozone supply line 76 toreduce the speed of the ozone gas.

[0037] A pressure detector 72 is connected to the exhaust line 58. Thepressure detector 72 can detect the pressure within the exhaust line 58,and therefore also the pressure within the enclosure 34.

[0038] A controller 80 is used for controlling various components of thesystem 10 shown in FIG. 1, including the pump 30, the ozone generator64, and the valves 68 and 70 shown in FIG. 2. The controller 80 receivesinput from the pressure detector 72 and controls all the componentsbased on the pressure detected by the pressure detector 72 and othervariables as will be described hereinbelow. The controller 80 istypically a computer having a processor which is programmed to execute aprogram which controls all the components of the system 10. The programincludes processor executable code and is typically stored on a disk orother computer readable medium and then loaded into memory of thecomputer from where the processor of the computer reads and executes theprogram to control the components of the system 10. Particular featuresof the program and how it is constructed will be evident to one skilledin the art from the discussion that follows.

[0039] Referring again to FIG. 1, it can be seen that each waferprocessing chamber 20A, 20B, or 20C leads directly off the transferchamber 18. A respective slitvalve 82A, 82B, and 82C is mounted to openor close communication between the transfer chamber 18 and a respectiveone of the wafer processing chambers 20A, 20B or 20C.

[0040] The cooldown chamber 22 also leads off the transfer chamber 18but no slitvalve is provided to open and close communication between thetransfer chamber 18 and the cooldown chamber 22.

[0041] A robot 84 is located within the transfer chamber 18. The robot84 has a blade 86 which, when the robot 84 is operated, can transfer awafer from one of the chambers 20, 22, or 24 to another. A susceptor 88is located in each one of the chambers 20 and 22, on which the wafer canbe located by the blade 86. The slitvalves 82 and the robot 84 are alsounder control of the controller 80 shown in FIG. 2.

[0042] One example of how the controller 80 controls the system 10 isnow described with reference to FIGS. 1 and 2 jointly. FIG. 3 is a flowchart which assists in illustrating how the system 10 is operated.

[0043] The slitvalves 42 are initially closed so that the confines ofthe transfer chamber 18 are not in communication with the loadlockchambers 24. The loadlock chamber 18 is initially evacuated to removecontamination. The loadlock chamber 18 is then backfilled with an inertgas such as nitrogen. The slitvalves 82 are open so that the waferprocessing chambers 20 are in communication with the transfer chamber18. The transfer chamber 18, the wafer processing chamber 20, and thecooldown chamber 22 are filled with an inert gas such as nitrogen gasand are at atmospheric pressure. The door 40 of the first loadlockassembly 14A is open.

[0044] A robot (not shown) located within the factory integration unit12 then loads a total of twenty-five wafers on the wafer cassette 28 ofthe first loadlock assembly 14A. (Step 1). The door 40 is then closed sothat the wafers 52 are isolated within the loadlock chamber 24. (Step2).

[0045] The pump 30 is then switched on so that air passes from theenclosure 34 through the exhaust line 58 through the pump 30. (Step 3).The valves 68, and 70 are closed so that the enclosure 34 is pumped downto a pressure of about 5 Torr.

[0046] The pump 30 is then switched off. (Step 4). The valve 68 is thenopened. (Step 5). Nitrogen then flows into the enclosure 34 until thepressure within the enclosure 34 is substantially the same as thepressure within the transfer chamber 18. The valve 68 is then closed.(Step 6).

[0047] The slitvalve 42 is then opened. (Step 7). The robot 84 thenremoves three wafers consecutively from the wafer cassette 28 andlocates one wafer within the first wafer processing chamber 20A, anotherwafer within the second wafer processing chamber 20B, and a furtherwafer within the third wafer processing chamber 20C. (Step 8). Theslitvalves 82 are then closed so that the wafer processing chambers 20are isolated from the transfer chamber 18. (Step 9). An epitaxialsilicon layer is then formed on the wafer in each processing chamber 20.(Step 10). A mixture of gasses is introduced into each one of the waferprocessing chambers 20. One of these gasses typically includes hydrogen.Another one of the gasses is a source of silicon such as silane,dichlorosilane, or trichlorosilane. The source of silicon reacts withthe hydrogen to form an epitaxial layer. Another one of the gasses istypically B₂H₆ which provides boron for purposes of doping the epitaxialsilicon layer. Heat lamps (not shown) heat the wafers within the waferprocessing chambers 20 to a temperature of between 600° C. and 1300° C.

[0048] Once the formation of the epitaxial silicon layer on one of thewafers is finalized, the processing gasses within the respectivechambers 20 are replaced by pure hydrogen gas to purge the chambers 20.(Step 11). The respective slitvalve 82 is then opened. (Step 12). Therespective wafer is transferred, utilizing the robot 84, to the cooldownchamber 22. (Step 13). Transfer of the wafer takes about twenty seconds.The wafer remains within the cooldown chamber 22 for about sixtyseconds. (Step 14). The robot 84 then transfers the wafer from thecooldown chamber 22 back to the wafer cassette 28. (Step 15). The waferis thus transferred from the chambers 20 to the wafer cassette 28without ever being exposed to oxygen or any other gas that can form anoxide on the epitaxial silicon layer.

[0049] The process of forming an expitaxial silicon layer on each waferis continued until all the wafers are processed in a similar manner andall the wafers are located back on the wafer cassette 28. It takesbetween one and two hours to process twenty-five wafers when forming a 5micron thick epitaxial silicon layer on each wafer. While the wafersfrom the first loadlock assembly 14A are processed, more wafers can belocated on the wafer cassette 28 of the second loadlock assembly 14B.

[0050] Once the wafers are located on the wafer cassette 28 of the firstloadlock assembly 14A, the slitvalve 38 thereof is closed. (Step 16).The wafers 52 are then typically at a temperature of less than 100° C.,but this temperature can vary depending on the time spent in thecooldown chamber 22.

[0051] The pump 30 is then again switched on so that nitrogen gas thenflows out of the enclosure 34. (Step 17). The enclosure 34 is pumpeddown to a pressure of about 5 Torr. The pump 30 is then switched off.(Step 18). The ozone generator 64 is then switched on and the valve 70is opened so that an ozone gas and oxygen gas mixture flows into the topof the enclosure 34. (Step 19). The ozone gas and oxygen mixturecontinues to flow into the enclosure 34 until the pressure within theenclosure 34 reaches about 600 Torr. The valve 70 is then closed and theozone generator 64 is switched off. (Step 20).

[0052] The wafers 52 are then simultaneously exposed to the ozone gaswithin the enclosure 34. Exposure of the epitaxial silicon layer on thewafer 52 results in oxidation of the epitaxial silicon layer. The wafers52 are exposed to the ozone gas for a period from one to fifteenminutes. The wafers 52 are simply “soaked” in the ozone gas i.e., thereare no additional sources of excitation which, for example, create aplasma or create certain photo effects. An oxide layer forms over theepitaxial silicon layer of each wafer and has a thickness of about 10 Åto about 15 Å, as measured by a multiple wavelength ellipsometrytechnique, for exposure to ozone gas of about fifteen minutes. The oxidelayer that forms on the wafer is extremely pure because of thecontrolled conditions to which the wafers 52 are exposed, including thepurity of the ozone gas and oxygen gas mixture to which the wafers 52are exposed.

[0053] As mentioned previously, hydrogen is used within the waferprocessing chamber 20. Hydrogen is highly explosive when mixed withozone or oxygen. However, for the hydrogen in the processing chambers 20to mix with the ozone within the enclosure 34, the system 10 has to failsimultaneously in a number of respects. First, there should be hydrogenwithin one of the wafer processing chambers 20. Second, the hydrogenshould leak past a respective slitvalve 82 of the relevant waferprocessing chamber 20. Leakage of hydrogen past the slitvalve 82 wouldonly occur if the slitvalve 82 does not seal sufficiently on the waferprocessing chamber or when the slitvalve 82 is not closed when hydrogenis introduced into the wafer processing chamber 20. Third, it isrequired that ozone be present within the enclosure 34. Fourth, ozoneshould leak from the enclosure 34 into the transfer chamber 18. Becausethe enclosure 34 is maintained at a pressure below that of the transferchamber 18, it is highly unlikely that there would be any flow of gassesfrom the enclosure 34 into the transfer chamber 18.

[0054] Furthermore, it should be noted that the pressure within theenclosure 34 never goes over atmospheric pressure so that there is asubstantially reduced likelihood that ozone gas can escape from theenclosure 34 to a surrounding area and cause exposure of personnel.

[0055] It should also be noted that, in the embodiment described, ozoneis only present within the apparatus 32 when generated by the ozonegenerator 64 which is only while the enclosure 34 is being filled withozone. There is therefore no contained source of ozone (other than inthe loadlock chambers 24) which may leak and cause exposure to personnelor other reactive gasses. Ozone gas is thus generated at the point ofuse.

[0056] The pump 30 is then again switched on so that the pressure withinthe enclosure 34 reduces to about 5 Torr. (Step 21). The ozone gasflowing through the pump 30 is pumped to a location distant from thesystem 10, where the ozone gas is neutralized. The ozone gas may forexample be neutralized by treatment with a chemical to form oxygen, bescrubbed in a fluidized bed of silica, or be scrubbed in another liquidsystem.

[0057] The valve 68 is then opened so that the enclosure 34 is filledwith nitrogen gas. (Step 22). The door 40 is then opened and the wafers52 are transferred from the enclosure 34 into the factory integrationunit 12. The factory integration unit 12 is filled with air. (Step 23).The air within the factory integration unit 12 does not form an oxidelayer on the epitaxial silicon layer because of the oxide layer which isalready formed thereon due to exposure to ozone.

[0058] It takes about twenty-five minutes to process the wafers withinthe first loadlock assembly 14A, as measured from when the slitvalve 42is closed until the wafers 52 are removed from the loadlock chamber 24.The time taken to process twenty-five wafers by the first loadlockassembly 14A is less than the time taken to process twenty-five waferswithin the wafer processing chambers 20 and cooling the wafer down inthe cooldown chamber 22, because the wafers are processed in batch.

[0059] As illustrated in FIG. 4 the first loadlock assembly 14A can thusbe used in an epitaxial silicon cycle wherein wafers are transferred tothe wafer processing chamber 20 and the cooldown chamber 22 andincluding every step from step 8 to step 16 in FIG. 3. The firstloadlock assembly 14A can then be used in a oxide cycle wherein thewafer is exposed to ozone gas and including every step from step 17 tostep 23 in FIG. 3. At the same time when the first loadlock assembly 14Ais used for an oxide cycle, the second loadlock assembly 14B can be usedfor a epitaxial silicon cycle, whereafter the second loadlock assembly14B can be used for an oxide cycle. When the second loadlock assembly14B is used in the oxide cycle, the first loadlock assembly 14A can beused in a epitaxial silicon cycle. It can thus be seen that, because theoxide cycles are shorter than the epitaxial silicon cycles, there is nolapse in time from one epitaxial silicon cycle to a next epitaxialsilicon cycle.

[0060]FIG. 5 illustrates a wafer 100 which is processed in accordancewith the invention. The wafer includes a monocrystalline substrate 102on which an epitaxial silicon layer 104 is formed. A silicon dioxidelayer 106 is formed on the epitaxial silicon layer 104. The silicondioxide layer can later be removed to leave the expitaxial silicon layer104 exposed and containing substantially no impurities. The silicondioxide layer can, for example, be removed in a aqueous solution ofhydrogen fluoride.

[0061]FIG. 6 and FIG. 7 illustrate the ozone generator 64 in moredetail. The ozone generator 64 includes a housing 120, two ultravioletlamps 122, four quartz tubes 124, an inlet pipe 126, and an outlet pipe128.

[0062] The housing 120 is leak tight and dust proof. A mirror 126 islocated on a lower surface of the housing 120.

[0063] The ultraviolet lamps 122 are located within the housing 120 on aside thereof opposing the mirror 126. Electrical connectors 128 extendinto the housing 120 to the ultraviolet lamps 122. The ultraviolet lamps122 can be energized by supplying electricity through the cables 128. Aleak tight interface exists between the housing 120 and the cables 128where the cables extend into the housing 120.

[0064] Each pipe 126 or 128 extends into the housing 120. A leak tightinterface also exists between each pipe 126 or 128 and the housing 120where the pipe 126 or 128 extends into the housing 120. The pipes 126and 128 are located on opposing sides of the housing 120 as can be seenin FIG. 7. The inlet pipe 126 has an inlet opening therein. The pipe 126interconnects ends of the tubes 124 to one another. The pipe 128 extendsthrough ends of the tubes 124 opposing the ends that are interconnectedby the pipe 126. Small openings 130 are formed in the pipe 128 withinthe tubes 124. Each opening 130 is typically about 2mm in diameter. Theopenings 130 are located facing away from a flow passage of a gasflowing through the tubes 126 so as to avoid a flow channel within eachtube 126 and to ensure mixing of a gas flowing through each tube 126.

[0065] The oxygen source 62 is connected to the inlet tube 126 through aregulator valve 132. The regulator valve 132 can be adjusted so as tocontrol flow to the inlet tube 126.

[0066] A nitrogen source 132 is connected to the housing 120. A p urgegas outlet 134 is also provided out of the housing 120.

[0067] Nitrogen from the nitrogen source 132 flows through the housing120 in an area around the tubes 124. The ultraviolet lamps 122 areswitched on by providing electricity through the cables 128. Oxygen fromthe oxygen source 62 flows through the regulator valve 132 and the pipe126 to the tubes 124. Ultraviolet light is transmitted by theultraviolet lamps 122. The quartz of the tubes 124 is transmissive sothat the ultraviolet light enters the tubes 124. One of the ultravioletlamps is located above two of the tubes 124 and another one of theultraviolet lamps 122 is located above another two of the tubes 124. Asubstantially equal amount of ultraviolet light enters the tubes 124because of substantially equal spacing of the lamps 122 over the tubes124. More ultraviolet light reflects from the mirror 126 and enters thetubes 124 from an opposing side. The ultraviolet light results in achange of some of the oxygen gas within the tubes 124 to ozone gas. Amixture of oxygen gas and ozone gas flows around the pipe 128 and leavesthe tubes 124 through the openings 130, from where the mixture flowsthrough the pipe 128 out of the housing 120. While ozone is formedwithin the tubes 124, the nitrogen in the area around the tubes 124suppresses ozone generation outside of the tubes 124. This reducesexposure of ozone to people, thereby making the ozone generator 64 safeto operate, and reduces the chance of ozone degradation of components ofthe ozone generator 64 located externally of the tubes 124.

[0068] The openings 130 are restrictions in the path of the mixture ofoxygen and ozone leaving the tubes 124. Because of the restrictionsprovided by the openings 120, free flow of gas through the tubes 124 isrestricted. Because of restrictions provided by the openings 120, thegas remains within the tubes 124 for longer and the flow thereof is moreevenly distributed between the tubes 124. The residence time of themixture within the tubes 124 is also increased.

[0069]FIG. 8 is a graph of ozone generation. A horizontal axis of FIG. 8is the rate at which the loadlock chamber is filled in Torr per minute.The higher the valve on the horizontal axis, the faster the loadlockchamber will be filled. A backfill rate of 60 Torr per minute, forexample, means that the loadlock chamber is filled to 600 Torr within 10minutes. The loadlock is preferably filled to 600 Torr within 20 minutesto maintain throughput, i.e. the rate on the horizontal axis ispreferably at least 30.

[0070] A vertical axis of the FIG. 8 graph is ozone concentration inparts per million. It can be seen from the graph that the ozoneconcentration is higher for lower filling rates of the load lockchamber. Furthermore, there is an appreciable increase in ozoneconcentration for filling rates below 50 (i.e. a filling time of morethan 12 minutes). The filling rate is therefore preferably between 20Torr per minute and 50 Torr per minute for purposes discussed withreference to FIG. 8 alone.

[0071]FIG. 9 is a graph of encapsulation of a wafer with an oxide formedwith ozone gas. A horizontal axis of the FIG. 9 graph is the ozoneconcentration in parts per million and the vertical axis is oxidethickness as measured with a single wavelength ellipsometry technique.The wafer is maintained at about room temperature and is exposed to theair and ozone gas mixture for 12 minutes. There is an increase in oxidethickness with ozone concentration up to an ozone concentration of about400 parts per million. In order to obtain an oxide thickness which issufficiently thick the ozone concentration is preferably at least 250parts per million. From FIG. 9 can thus be gathered that the ozoneconcentration is preferably between 250 parts per million and 350 partsper million. Referring again to FIG. 8, it can be seen that such anozone concentration requires a filling rate of between 33 Torr perminute and 45 Torr per minute. In order to maintain an ozoneconcentration of at least 250 parts per million and an appreciable oxidethickness, the loadlock is preferably filled at a rate of about 45 Torrper minute.

Single-Wafer Exposure to High Concentration Levels of Ozone Gas Suitablefor Epitaxial Silicon Deposition on Small or Large Numbers of Wafers

[0072]FIG. 10 illustrates a portion of a loadlock assembly 200 accordingto another embodiment of the invention. The loadlock assembly 200includes a loadlock chamber 202 and an ozone generator 204.

[0073] The loadlock chamber 202 includes a chamber body 206 and a window208. The window 208 is secured to the chamber body 206. An enclosure 210is defined within the loadlock chamber 202. An inner surface of thechamber body 206 defines a portion of the enclosure 210 and an innersurface of the window 208 also defines a portion of the enclosure 210.The window 208 is transmissive to ultra-violet radiation and has aplurality of small ozone gas openings 212 formed therein.

[0074] The ozone generator 204 includes a block body 216 which issecured to the chamber body 206. The block body 216 has defined thereinan ozone generation chamber 218. Small air inlet openings 220 are formedthrough one side of the block body 216 into the ozone generation chamber218. A slot 221 is formed from the ozone generation chamber 218 out ofthe block body 216 on a side thereof opposing the air inlet openings220. The slot 221 is located over the window 208.

[0075] The ozone generator 204 also includes an ultraviolet source lamp222. The ultraviolet source lamp 222 is located within the ozonegeneration chamber 218. FIG. 11 is a view on 11-11 in FIG. 10 andillustrates that the ultraviolet source lamp 222 has a filament 224 anda terminal 226. The terminal is connected to the filament 224 so thatelectric current can be provided through a terminal 226 to the filament224. The terminal 226 is located externally of the block body 216 and aseal 228 is located between a surface of the ultraviolet source lamp 222and the block body 216 to prevent gas from escaping from within theozone generation chamber 218. The filament 224, when electric currentflows therethrough, creates ultraviolet radiation, according to knownprinciples in the art. The openings 220 are evenly spaced over the widthof the block body 216. The openings 212 in FIG. 10 have an arrangementthat is similar to the openings 220.

[0076] In use, a wafer 230 is located in a horizontal plane with acenter line thereof substantially at the same elevation as the ozone gasopenings 212. An electric current is then provided through the terminals226 to the filament 224 so that the filament 224 creates ultravioletlight 232A and 232B. The ultraviolet light 232A and 232B radiateshorizontally through the slot 221 and then through the window 208. Theultraviolet light 232A then radiates horizontally over an upper surfaceof the wafer 230 and the ultraviolet light 232B radiates horizontallyover a lower surface of the wafer 230. The light 232A and 232B radiatesparallel to upper and lower surfaces of the wafer 230.

[0077] Air 240 is introduced through the air inlet openings 220 into theozone generation chamber 218. The air flows over the ultraviolet sourcelamp 222 into the slot 221. Ultraviolet light radiating from theultraviolet source lamp 222 into the ozone generation chamber 218converts a first amount of the oxygen to a first amount of ozone gas. Agas flowing from the slot 221 into the ozone gas openings 212 includes amixture of unconverted air and the first amount of ozone gas.

[0078] The air then flows from the ozone gas openings 212 into theenclosure 210 over upper and lower surfaces of the wafer 230. The upperand lower surfaces of the wafer 230 are thereby exposed to the firstamount of ozone gas (generated in the ozone gas generation chamber 218).

[0079] As the gas flows over the wafer 230 the first amount of ozone gasdepletes. Such depletion of the first amount of ozone gas could lead toa lower rate of sealing of surfaces of the wafer 230 located distantfrom an edge 242 thereof closest to the ozone gas openings 212. However,the ultraviolet light 232A and 232B radiates through the remainder ofthe first amount of ozone gas and the unconverted air, therebyconverting the unconverted air to a second amount of ozone gas whilelocated over surfaces of the wafer 230. The second amount of ozone gas,that is continuously being generated, maintains a concentration of ozonegas relatively high. Sealing rates of portions of surfaces of the wafer230 located distant from the edge 242 are thereby maintained high.

[0080]FIG. 12 represents concentrations of gasses located within theloadlock assembly 200. The gas is initially entirely air as it entersthe air inlet openings 220. The concentration of ozone gas thenincreases and the concentration of air decreased until the gasses leavethe ozone gas openings 212. The concentration of these gasses thenremain constant until they reach the edge 242 of the wafer 230. Theconcentration of ozone gas in these gasses then depletes as it flowsover the wafer 230. However, ozone gas is also generated in the loadlockchamber 202 by the ultra-violet light 232A and 232B. The concentrationof the ozone gas generated in the loadlock chamber 202 increases as thegasses flow over the wafer 230. The total concentration level of theozone gas thereby remains relatively constant as the gasses flow overthe surfaces of the wafer 230.

[0081]FIGS. 13 and 14 illustrate further components of the loadlockassembly 200. FIG. 13 is a view similar to FIG. 2 and the similaritiesshould be evident. FIG. 14 is a view in a direction 250 in FIG. 13.

[0082] The loadlock chamber 202 is smaller than the loadlock chamber 24of FIG. 2. A wafer cassette 252 is also provided but can hold only twowafers 230A and 230B. Other components of the loadlock assembly 200 aresimilar to the components of the loadlock assembly 14 of FIG. 2. Theloadlock assembly 200 also includes a source of nitrogen 254 and anitrogen supply valve 256. A pump 258 is connected to the loadlockchamber 202. A controller 260 is responsive to a pressure detector 262and controls the valve 256 and the pump 258 in a manner similar ashereinbefore described with reference to FIG. 2.

[0083] Referring to FIG. 14 in particular, the loadlock assembly 200further includes a power source 270, a switch 272, and an air valve 274.The terminal 226 of the ultraviolet source lamp 222 is connected throughthe switch 272 to the power source 270. The air valve 274 controls flowof air into the block body 216 of the ozone generator 204. Thecontroller 260 also controls operation of the switch 272 and the valve274.

[0084] It can thus be seen that a first amount of ozone gas is generatedoutside of the loadlock chamber 202 and, in addition, a second amount ofozone gas is generated within the loadlock chamber 202 therebymaintaining ozone gas concentrations high. High concentrations of ozonegas allow for a wafer to be sealed at a higher rate utilizing theloadlock assembly 200 than when using the loadlock assembly 14 of FIG.2. As previously mentioned with reference to FIG. 4, an ozone cycleutilizing a batch loadlock system takes about 25 minutes. However,because of higher concentrations of ozone gas utilizing the loadlockassembly 200, a wafer can be sealed in as little as 1 minute. Fastsealing of a wafer allows for more flexibility in operation of a system.For example, should only two wafers have to be processed, and each wafertakes about 3 minutes to process in a respective processing chamber, onewafer can then be located in a loadlock chamber 202 and be sealed for 1minute, whereafter the other wafer can be located in the loadlockchamber 202 and be sealed for another minute. The total processing timeof both wafers would then be 5 minutes. However, utilizing a batchloadlock such as the system of FIG. 2, it would take 3 minutes toprocess the two wafers in processing chambers and another 25 minutes toseal them thus totaling 28 minutes.

[0085] The system 10 of FIG. 1 can be modified by replacing the loadlockassemblies 14A and 14B with loadlock assemblies such as the loadlockassembly 200. Only the chambers 20B and 20C need to be used forepitaxial silicon formation.

[0086]FIG. 15 illustrates one method in which the system such as thesystem 10 in FIG. 1 having two loadlock chambers 202A and 202B can beused for wafer processing. Each loadlock chamber 202A or 202B forms partof a respective loadlock assembly such as the loadlock assembly 200. Instep 301 the loadlock chambers 202A and 202B are opened to atmosphere sothat they are filled with air, a wafer 1A is located in the loadlockchamber 202A, and another wafer 2A is located in the loadlock chamber202B. In step 302 the loadlock chambers 202A and 202B are closed andfilled with nitrogen gas, and in step 303, the wafers 1A and 2A aremoved into the processing chambers 20B and 20C respectively. In steps304, 305, and 306, two more wafers 1B and 2B are located in the loadlockchambers 202A and 202B respectively, as in the steps 301, 302, and 303.

[0087] In step 307, the wafers 1A and 2A are moved back into theloadlock chambers 202A and 202B, respectively. The wafers 1A and 2A arelocated at the top and the wafers 1B and 2B are located at the bottom.In step 308, the wafers 1B and 2B are moved into the processing chambers20B and 20C so that only the wafers 1A and 2A in the loadlock chambers202A and 202B. Epitaxial silicon is formed on the wafers 1A and 2A whilethey were located in the processing chambers 20B and 20C. The wafers 1Aand 2A are ready to be sealed with ozone gas. The cassette holding thewafers 1A and 1B is moved so that the wafer 1A is in line with ozone gasopenings in a window of the loadlock chamber 202A. Similarly, thecassette holding the wafers 2A and 2B is moved so that the wafer 2A isin line with ozone gas openings of a window of the loadlock chamber202B.

[0088] In step 309 the loadlock chambers 202A and 202B are filled withozone gas and the ultraviolet source lamps of the loadlock assembliesare switched on. The epitaxial silicon layers on the wafers 1A and 2Aare thereby sealed with an oxygen layer.

[0089] In step 310, the loadlock chambers 202A and 202B are opened toatmosphere, and in step 311, the wafers 1A and 2A are removed from theloadlock chambers 202A and 202B. Step 311 is the same as step 304,except that the wafers 1A and 2A are replaced with the wafers 1B and 2B,respectively. The steps following step 304 can then again be carried outwith following wafers. FIG. 15 therefore illustrates how a cassette anda respective one of the loadlock chambers 202A or 202B, holding twowafers 1A and 1B, or 2A and 2B, can be used.

[0090]FIG. 16A and 16B illustrates a method wherein only one shelf isrequired in a respective loadlock chamber 202A or 202B. In steps 401,402, 403, and 404, the loadlock chamber 202A is open to atmosphere, awafer 1 is located therein, the loadlock chamber is filled with nitrogengas, the wafer 1 is moved into the processing chamber 20B, and theloadlock chamber 202A is again opened to atmosphere. In steps 405, 406,407, and 408, another wafer 2 is located in the loadlock chamber, theloadlock chamber is filled with nitrogen gas, the wafer 2 is moved intothe processing chamber 20C, and the loadlock chamber 202B is againopened to atmosphere. Epitaxial silicon layers are formed on the wafers1 and 2 while located in the processing chambers 20B and 20C,respectively.

[0091] In step 409 another wafer 3 is located in the loadlock chamber202A. In step 410, the wafer 1 is sealed utilizing ozone gas and theultraviolet source lamp that radiates over the wafer 1. In step 411, thewafer 3 is moved into the processing chamber 20B. In step 412, the wafer2 is moved into the loadlock chamber 202A. In step 413, the wafer 1 isremoved from the loadlock chamber 202B, and the wafer 2 is sealed in theloadlock chamber 202A. In steps 414, 415, and 416, the loadlock chamber202B is again filled with nitrogen gas, and the wafer 2 is removed outof the loadlock chamber 202A. The system following step 416 is the sameas the system following step 404, except that the wafer 1 is replacedwith the wafer 3. The step following step 404 can then again be repeatedfor subsequent wafers.

[0092] While certain exemplary embodiments have been described and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative and not restrictive of the currentinvention, and that this invention is not restricted to the specificconstructions and arrangements shown and described, since modificationsto either of the above embodiments may occur to those ordinarily skilledin the art. In another embodiment an ozone source may, for example, be acontained source of ozone located externally of a loadlock chamber. Inanother embodiment, an ozone source such as an ozone generator may, forexample, be located within a loadlock chamber.

What is claimed:
 1. A method of processing a wafer, which includes: (a)locating a wafer in a wafer processing chamber of a system forprocessing a wafer; (b) forming a silicon layer on the wafer whilelocated in the wafer processing chamber; (c) transferring the wafer fromthe wafer processing chamber to an ozonification chamber of the systemwhile remaining substantially unexposed to air; (d) closing offcommunication between the processing chamber and the ozonificationchamber; (e) allowing a first amount of ozone gas into the ozonificationchamber; (f) exposing the wafer to the first amount of ozone gas whilelocated in the ozonification chamber; (g) radiating ultraviolet lightthrough an unconverted gas in the ozonification chamber therebyconverting the unconverted gas to a second amount of ozone gas; (h)exposing the wafer to the second amount of ozone gas while located inthe ozonification chamber; and (i) removing the wafer from theozonification chamber.
 2. A method according to claim 1 wherein theozonification chamber is a loadlock chamber and in step (i) the wafer isremoved out of the system.
 3. A method according to claim 1 whichincludes: (j) generating the first amount of ozone gas in an ozonegeneration chamber that is in communication with the ozonificationchamber.
 4. A method according to claim 3 wherein the first amount ofozone gas is generated by radiating ultraviolet light through anunconverted gas in the ozone generation chamber.
 5. A method accordingto claim 4 wherein the ultraviolet light radiating through theunconverted gas in the ozone generation chamber and the ultravioletlight radiating through the unconverted gas in the ozonification chamberoriginate from a common source lamp.
 6. A method according to claim 5wherein, when step (f) and step (h) are carried out, a pressure withinthe ozonification chamber is below a pressure in the wafer processingchamber.
 7. A method according to claim 2 wherein, when step (f) andstep (h) are carried out, a pressure within the loadlock chamber isbelow a pressure in the wafer processing chamber.
 8. A method accordingto claim 1 wherein hydrogen gas is present within the processing chamberat any given time between when (e) is started and (h) ends.
 9. A methodaccording to claim 8 wherein the pressure within the loadlock chamberremains below atmospheric pressure from (e) to (h).
 10. A methodaccording to claim 1 wherein substantially no oxide layer forms on thesilicon layer before exposure to the ozone gas.
 11. A method ofprocessing a wafer, which includes: (a) locating a wafer in a waferprocessing chamber of a system for processing a wafer; (b) forming asilicon layer on the wafer while located in the wafer processingchamber; (c) transferring the wafer from the wafer processing chamberthrough a first opening of a loadlock chamber into the loadlock chamberof the system while remaining substantially unexposed to air; (d)closing off communication between the processing chamber and theozonification chamber; (e) allowing oxygen gas into an ozone generationchamber; (f) conducting current through a filament of an ultravioletlight in the ozone generation chamber thereby converting some of theoxygen gas to a first amount of ozone gas; (g) allowing the first amountof ozone gas together with oxygen gas through an opening in a windowinto the loadlock chamber; (h) exposing the wafer to the first amount ofozone gas while located in the loadlock chamber; (i) radiatingultraviolet light from the filament through the window and then throughthe oxygen gas in the loadlock chamber thereby converting the oxygen gasin the loadlock chamber to a second amount of ozone gas; (j) exposingthe wafer to the second amount of ozone gas while located in theloadlock chamber; and (k) removing the wafer through a second opening ofthe loadlock chamber from the loadlock chamber.
 12. A system forprocessing a wafer comprising: an ozonification chamber defining anenclosure and having at least a first opening for transferring a wafertherethrough from an area externally of the ozonification chamber intothe enclosure; a wafer holder located within the ozonification chamberto hold the wafer in the enclosure; an ozone source system having anozone-containing chamber in communication with the enclosure so that afirst amount of ozone gas flows from the ozone-containing chamber intothe enclosure and the wafer held by the wafer holder is exposed to thefirst amount of ozone gas, the ozone source system including at leastone ultraviolet lamp having a filament which, when electric currentflows therethrough creates ultraviolet light, the ultraviolet lighttherefrom radiating through a second amount of unconverted gas in theenclosure so that the second amount of unconverted gas is converted to asecond amount of ozone gas and the wafer held by the wafer holder isexposed to the second amount of ozone gas.
 13. The system of claim 12wherein the chamber includes a chamber body and a window, that istransmissive to ultraviolet light, the chamber body and the windowjointly forming the chamber, the ultraviolet lamp being locatedexternally of the chamber and ultraviolet light therefrom radiatingthrough the window and then through the second amount of unconvertedgas.
 14. The system of claim 13 wherein the ozone containing chamber islocated externally of the chamber.
 15. The system of claim 14 whereinthe ozone-containing chamber is an ozone generation chamber andultraviolet light radiates through a first amount of unconverted gas inthe ozone generation chamber so that the first amount of unconverted gasis converted to the first amount of ozone gas that flows from the ozonegeneration chamber into the enclosure.
 16. The system of claim 15wherein light from one ultraviolet lamp converts the first amount ofunconverted gas to the first amount of ozone gas and converts the secondamount of unconverted gas tot the second amount of ozone gas.
 17. Thesystem of claim 12 wherein the light radiating through the second amountof unconverted gas radiates substantially parallel to a plane of thewafer over a first surface of the wafer.
 18. The system of claim 17wherein the light radiating through the second amount of unconverted gasradiates substantially parallel to a plane of the wafer over a secondsurface of the wafer opposing the first surface.
 19. The system of claim12 wherein the chamber is a loadlock chamber having a second opening fortransferring the wafer therethrough from the enclosure and an areaexternally of the loadlock chamber.
 20. The system of claim 19, whichincludes: a wafer processing chamber; a closure member which is movablebetween a first position which allows for a wafer to be transferred fromthe wafer processing chamber into the loadlock chamber, and a secondposition wherein the closure member substantially closes offcommunication between the loadlock chamber and the wafer processingchamber; and a pump having a low-pressure side connected to the loadlockchamber.
 21. A system according to claim 20 which includes a transferchamber leading off the loadlock chamber, and a plurality of waferprocessing chambers leading off the transfer chamber, the wafer beingtransferred from the wafer processing chamber through the transferchamber to the loadlock chamber.
 22. A system according to claim 21wherein the loadlock chamber is a first loadlock chamber, and theclosure member is a first closure member, the system including: a secondloadlock chamber; a second wafer holder in the second loadlock chamberand capable of holding a wafer; and a second closure member which ismovable between a first position which allows for a wafer to betransferred from the wafer processing chamber through the transferchamber to the second loadlock chamber, and a second position whereinthe second closure member substantially closes off communication betweenthe second loadlock chamber and the transfer chamber.
 23. A systemaccording to claim 20 which includes a controller which has a processorexecutable code which controls the pump and the ozone source.
 24. Asystem according to claim 23 wherein the processor executable codemaintains the loadlock chamber at a lower pressure than on a side of theclosure member opposing the loadlock at all times when the wafer isexposed to the ozone gas.
 25. A system according to claim 24 wherein theprocessor executable code maintains the loadlock below atmosphericpressure at all times when the wafer is exposed to ozone gas.
 26. Asystem according to claim 24 wherein the processor executable code: (i)controls the closure member by opening the closure member; (ii) controlsa robot so that the robot then transfers the wafer from the waferprocessing chamber into the loadlock chamber; (iii) then closes theclosure member; and (iv) controls the ozone source by then exposing thewafer to the ozone gas when located in the wafer processing chamber. 27.A system for processing a wafer comprising: a chamber body; a window,that is transmissive to ultraviolet light, mounted to the chamber body,the chamber body and the window jointly forming a chamber, the chamberdefining an enclosure and having at least a first opening fortransferring a wafer therethrough from an area externally of the chamberinto the enclosure; a wafer holder located within the chamber to holdthe wafer in the enclosure; an ozone generation chamber locatedexternally of the chamber and being in communication with the enclosure;at least one ultraviolet lamp having a filament which, when electriccurrent flows therethrough creates ultraviolet light, the ultravioletlight therefrom radiating through a first amount of unconverted gas inthe ozone generation chamber so that the first amount of unconverted gasis converted to a first amount of ozone gas that flows from the ozonegeneration chamber into the enclosures and the wafer held by the waferholder is exposed to the first amount of ozone gas, and radiatingthrough the window and then through a second amount of unconverted gasin the enclosure so that the second amount of unconverted gas inconverted to a second amount of ozone gas and the wafer held by thewafer holder is exposed to the second amount of ozone gas.
 28. Thesystem of claim 27 wherein light from one ultraviolet lamp converts thefirst amount of unconverted gas to the first amount of ozone gas andconverts the second amount of unconverted gas tot the second amount ofozone gas.
 29. The system of claim 27 wherein the light radiatingthrough the second amount of unconverted gas radiates substantiallyparallel to a plane of the wafer over a first surface of the wafer.